1. Field of the Invention
The present invention relates generally to methods of driving ink jet recording heads fit for use in general business machines such as printers, facsimile machines, ink jet recording apparatus and the like, and more particularly to a method of driving a recording head that has an ink tank as an integrated part, or most suitably that is removable from a recording apparatus itself.
2. Background Art
A thermal energy recording system which utilizes film boiling in conventional ink jet recording heads and apparatus is superior to what utilizes piezoelectric elements and has been put in practical use as superior to thermal energy recording using optical energy.
It is also well known that a recording head has a specific range of driving frequencies provided the recording head is configured as prescribed and that recording will be accomplished without any problem if driving conditions in that range are given.
Although such a recording head satisfies predetermined response characteristics, there may arise a case where the recording has to be made under the condition beyond its characteristics. Moreover, some of the recording characteristics are seen to deteriorate when those which ought to be stable are affected unfavorably. FIGS. 2 and 3 illustrate the problems addressed by the present invention. Arrows in these drawings designate the relative direction in which the recording head and recording paper move. As illustrated, the recording head has 32 discharge ports in the vertical direction, showing partitions of characters formed with a 32.times.32matrix. Numeral 6 in FIG. 2 shows a part in which a recording line is formed with substantially two liquid droplets (equivalent to a minimum recording unit). The part 6 normally poses no problem when a character is formed. However, the printing density in this part of an image tends to become slightly thin or blurred in comparison to the remaining part.
In the case of rotary printing for use in word processors, on the other hand, the number of parts to be formed by two droplets with respect to the relative direction of movement shown by the arrow is seen to increase greatly as shown in FIG. 3. Although the problem posed in reference to FIG. 3 is not always common to all recording parts formed with substantially two droplets (a minimum recording unit) , relatively many density-reduced parts 17 equivalent in position to the 23rd and 32nd discharge ports are produced even with a similar recording head. When no problem is associated with the part 17, a slight reduction in density may be observed in a part 16 equivalent to the first to fourth discharge ports on some occasions.
Moreover when about two droplets (a minimum recording unit) concentrate on the boundary region between the character partitions, an adjoining character-forming partition is infected with a small amount of droplet which may lower the whole image quality. High-density character formation at relatively high speed may sometimes cause the number of density-reduced parts to gradually increase and a serious problem may consequently be induced with the parts ignorable from the initial general image quality as a trigger.
In the case of a recording head which has incorporated an ink tank into a head portion and is removable from the recording apparatus(i.e. replaceable therefrom), a serious problem still arises from the fact that a reduction in density precariously occurs when the suction pressure of a sponge fluctuates as natural force deriving from capillarity is relied upon against the suction pressure of the sponge as an absorber in the ink tank. In order to solve this problem, an attempt may be made to lower the suction pressure of the sponge to eliminate the influence thereof; however, it still remains unpractical as leakage of ink from the ink tank is induced.